1. Field of the Invention
This invention relates to a catheter for diagnostic procedures such as transillumination or for therapeutic procedures such as inducing localized hyperthermia and/or photodynamic therapy in a patient and, more particularly, to a catheter for the transluminal or intersitial delivery of heat to tissue.
2. Prior Art
The use of light sources such as lasers has become common in the medical industry. As new, higher power light sources are created providing wavelengths useful for medical applications, the indications for use have increased dramatically. One such application is the delivery of diffuse light energy in energy densities sufficient to cause hyperthermia (elevated tissue temperature), photocoagulation (to weld or destroy tissue depending upon the degree of temperature increase), inducing a photodynamic/photobiological effect or performing diagnostic transillumination for imaging tissue. Current art light delivery devices are available to either diffuse or focus light in a forward direction to effect a light/tissue interaction. One limitation of these devices is that the tissue being heated develops a temperature gradient which is greatest at the interface closest to the light delivery system and decreasing with the depth of the tissue as described by thermal and light diffusion theory. Certain medical applications require a temperature field much different than this model.
Adjunctive hyperthermia, the use of deep heating modalities to treat hyperproliferating cells such as tumors, is finding increasing use for synergistically improving the effectiveness of Photodynamic Therapy (PDT), chemotherapy and radiative therapy in cancer treatment. Unfortunately, current hyperthermia devices for intraluminal delivery are not able to deliver localized heat to a target tissue located adjacent to a tubular tissue without damaging the luminal wall of the tubular tissue. In addition to the above described thermal field problem, prior art intraluminal, optically-induced hyperthermia devices cannot sufficiently couple the light energy out to the target tissue. As the light energy or power in the delivery device increases, the greater the chance that the delivery device will fail. Cooling the delivery device also permits the efficient coupling of the light energy out of the delivery device enabling the operation of the light guide at much greater power levels.
It is, therefore, desirable that a catheter is available which provides intraluminal delivery of light to a target tissue adjacent to the lumen which produces a thermal gradient which is substantially uniform in the target tissue or at least not excessive at the interface which is closest to the delivery device and which has the capacity to handle high power when required.